Characterization of Apple Juice Foams for Foam-mat Drying Prepared with Egg White Protein and Methylcellulose

RAHARITSIFA, NARINDRA; GENOVESE, DIEGO B.; RATTI, CRISTINA

JOURNAL OF FOOD SCIENCE

Blackwell Synergy

Año: 2006 vol. 71 p. 142 - 151

0022-1147

Foams were prepared from clarified apple juice by adding various concentrations of two foaming agents of different nature: a protein (egg white at 0.5, 1, 2 and 3% w/w) and a polysaccharide (methylcellulose at 0.1, 0.2, 0.5, 1 and 2% w/w), and whipping at different times (3, 5 and 7 minutes). In general, egg white foams were less stable, but showed higher degree of solidity (stronger structures), higher foaming capacity, and smaller bubble average diameter than methylcellulose foams. Foam stability increased with increasing concentrations of either methylcellulose or egg white. Increasing whipping times increased the stability of egg white foams only. Stability parameters (maximum drainage and drainage half time) were correlated in terms of rheological parameters of the continuous phase (consistency index and apparent viscosity at 30s-1, respectively). The correlations (R2 = 0.766 and 0.951, respectively) were considered acceptable since they were independent of whipping time, foaming agent nature and concentration. Results on foam rheology obtained by dynamic and vane tests were in agreement, but the latter method was more sensitive. Optimal concentrations to obtain the most solid foams (0.2% methylcellulose and 2-3% egg white, respectively) were the same concentrations required for maximum foaming capacity. Based on this observation and previous models, an empirical expression was proposed to predict the degree of solidity (in terms of inverse phase angle and yield stress) only as a function of foam structural properties (air volume fraction and average bubble size). The model proved to be satisfactory to fit experimental results (R2 = 0.848 and 0.975, respectively), independently of whipping time, foaming agent nature and concentration.